1. Field of the Invention
The present invention relates to an availability evaluating system for evaluating an availability of a semiconductor manufacturing line which includes a plurality of semiconductor manufacturing tools and a semiconductor manufacturing line design system for designing a semiconductor manufacturing line with a high availability.
2. Description of the Related Art
In a semiconductor manufacturing line for fabricating a semiconductor device such as an LSI, it is necessary to equip a plurality of semiconductor manufacturing tools for forming a very small transistors, for example, and further, form metal wirings by applying a variety of processing operations onto a semiconductor substrate. There are several tens or more of processing types for manufacturing a semiconductor device. The same type of processing, for example, wet cleaning processing is carried out a plurality of times until a semiconductor device has been completed. Thus, a semiconductor device is completed through processing steps of several hundreds times in total. Processing type is divided on a step by step basis, and a dedicated semiconductor manufacturing tool is provided in accordance with each step. In order to construct a semiconductor manufacturing line, first, fabrication procedures (a process flow) are determined by a design; type and number of a fabrication tool required to achieve this manufacturing line are determined; and the required fabrication tools are allocated in a clean room. Then, it becomes possible to fabricate a semiconductor device by establishing a processing condition.
In one step of a conventional semiconductor manufacturing line, for example, there is used a semiconductor manufacturing tool for processing 25 wafers (one lot) of 200 mm-diameter by one unit for one hour. Assuming that an operating time of this fabrication tool for one month is 720 hours, this semiconductor manufacturing tool has a large processing capability such that the number of wavers which can be processed for one month is 25×720=18,000 wafers, and the number of lots is 720. In one process flow, one fabrication tool may be used to process only one step or a plurality of steps in the flow according to a processing event. In the case where the semiconductor manufacturing tool previously described as an example processes a plurality of steps in one process flow, the processing capability in each step becomes several thousands of wafers per month (i.e., several hundreds of lots per month). In general, a semiconductor manufacturing process including several hundreds of steps is required in a production scale of 25,000 wafers per month. In the case of using a semiconductor manufacturing tool having the above processing capability, a total number of several hundreds of tools may be used. This total number is obtained from 25,000 wafers per month×several hundreds of steps/18,000 per month for each tool. Therefore, a total number of several tens of tools is necessary in a production scale of 2,500 wafers per month.
In construction of the conventional semiconductor manufacturing line, based on such estimation, a variety of fabrication tools are introduced into the line; each fabrication tool is actually operated; and the fabrication availability of the entire line is finally obtained. When the thus obtained fabrication availability fails to reach a target, a predetermined fabrication availability has been obtained by adding a required number of bottleneck fabrication tools (refer to, for example, Y. Mikata et al; Proceedings of ISSM2001, p7). In a manufacturing line of 25,000 wafers per month, several to some tens of fabrication tools may have a processing function of the same event, and a plurality of tools may be allocated as a dedicated tool or tools for processing a specific step. In this line, even if one tool down occurs, as long as other tools capable of processing the same processing operate, the fabrication availability of the line is hardly affected by such a tool down.
In the semiconductor manufacturing line, there exists a case in which only one fabrication tool is allocated for one processing event (in this case, referred to as an only one-tool unit) or a case in which two or three fabrication tools (a two-too unit or three-tool unit) having the same processing function are allocated to one processing event, as described above. If such a one-tool unit stops, the fabrication availability of the line is greatly affected. However, even if one tool of the two-tool unit or three-tool unit is down or stops, the remaining tool or tools still operate. Thus, no lot flow stoppage occurs, but an effect on the fabrication availability of the line cannot be ignored. In this way, in the one-tool unit, two-tool unit, three-tool unit and the like, an effect on the line fabrication availability when a configuration tool stops must be considered. Conventionally, there has not been provided a technique capable of simply evaluating such an effect.
In contrast, in the line of 2,500 wafers per month, there are many cases in which respective one fabrication tool is allocated to each of plural types of steps, and it is possible to carry out all of processing in a plurality of steps of one type which is targeted to be processed by such one tool. In such a line composed of one-tool units, even if any of such only one-tool units stops, the lot flow or movement of wafers to a next step will stop. Therefore, the line fabrication availability greatly depends on the availability of the one-tool unit. Conventionally, after a semiconductor device manufacturing line has been constructed, and after the fabrication availability of an actual line has been verified, countermeasure has been taken against a unit in a bottleneck step. Specifically, countermeasure is taken by increasing the number of tools in a bottleneck step, i.e., by providing a two-tool unit, for example, instead of an only one-tool unit. However, when a plural-tool unit such as a two-tool unit or a three-tool unit is provided, the number of fabrication tools for carrying out the same processing must be increased. A total number of tools per line increases, thus having caused an increase of tool investment, an increase of running cost, and an increase of clean room space.
As described above, various types of fabrication tool units are provided in a semiconductor device manufacturing line, and an only one-tool unit, a two-tool unit, a three-tool unit and the like are provided for a processing event. From among them, it has been extremely difficult to evaluate an availability of a line in consideration of an effect on the line fabrication productivity when one or more tools stop(s). In addition, one-tool units are mainly provided in a small scale semiconductor manufacturing line, and thus, the lowering of the line availability caused by a failure of such a one-tool unit has been a large problem.